Nerve terminals in human periodontal ligament as demonstrated by immunohistochemistry for neurofilament protein (NFP) and S-100 protein.

Nerve terminals in the human periodontal ligament were investigated by immunohistochemistry for neurofilament protein (NFP) and glia-specific S-100 protein. The human periodontal ligament was found to be innervated by NFP-immunoreactive nerve fibers, and contained free and specialized nerve endings; essentially all these nerve fibers were associated with S-100 protein-immunoreactive elements. Free nerve endings showing tree-like ramifications were frequently observed along the whole length of the tooth. The specialized nerve endings consisting of thick nervous elements were classified into four types as follows: Ruffini-like endings which were composed of expanded nerve terminals arranged in a dendritic fashion were found mainly around the root apex; coiled nerve endings were located in the mid-region of the periodontal ligament; spindle-shaped types, and expanded nerve endings, both rarely found near the root apex. Immunostaining for S-100 protein showed that no lamellated nerve terminals were found in the human periodontal ligament. The region-specific distribution of various nerve terminals demonstrated in this study seems to be suited to effectively receive mechanical stimuli to the teeth from various directions.